Graded-composition buffer layers using digital AlGaAsSb alloys

Abstract

We describe step-graded digital-alloy buffers using alternate layers of Al0.5Ga0.5As and Al0.5Ga0.5As0.65Sb0.35 grown on GaAs substrates by molecular beam epitaxy. The buffers consist of three sets of superlattices with AlGaAs/AlGaAsSb layer thicknesses of 7.7/2.3 nm, 5.4/4.6 nm, and 3.1/6.9 nm, respectively, terminating in a lattice constant equal to that of bulk In0.32Ga0.68As. Transmission electron micrographs show that most of the misfit-generated dislocations lie near the steps in pseudoalloy composition, and atomic force micrographs indicate a rms surface roughness of 3.6 nm. A 20.5-period lattice-matched InGaAs/InAlAs reflector stack grown on such a buffer has a peak reflectivity of 98% near 1.3 μm. These buffers provide potentially useful substrates for optoelectronic device applications near 1.3 μm using strained InGaAs active regions.

2.5–3.5 μm optically pumped GaInSb/AlGaInSb multiple quantum well lasers grown on AlInSb metamorphic buffer layers

“…Dislocation filtering with superlattices has been demonstrated with mobility studies in other material systems. 11 The ability of AlSb/GaSb superlattice to filter dislocations to produce an optically active region has been demonstrated by growing AlGaSb/GaSb double heterostructure lasers on silicon. 12 Figure 2 shows the flat band schematic for the laser structures grown on the metamorphic buffers.…”

InAlAs Graded Metamorphic Buffer with Digital Alloy Intermediate Layers

“…6) Also, overshoot 7) or reverse steps 8) in the graded buffer were proved beneficial for the full relaxation of residual strain, while Be doping 9) and dilute nitride buffers 10) were suggested to further reduce the TD density. Moreover, a built-in strain field, which arises from strained 11) or strain-compensated supperlattice (SL) 12) and strain-driven quantum dots, 13) was reported to bend the dislocation propagation and thereby decrease the TD density. Recently, a digital alloy (DA) has been applied as an option for the growth of ternary or quaternary materials of various compositions by molecular beam epitaxy (MBE), without additional source cells or laborious growth interruption for cell temperature changes.…”

Novel pseudoalloy approach to epitaxial growth of complex InGaAlAs multilayer structures

“…Our approach is an extension of that work to include various combinations of ternary and quaternary alloys for the individual layers, an area in which little work has been done. 4 Of course, it is possible to grow any composition by switching among the three binary states, but in most instances this is not convenient because of the large lattice mismatch involved.…”